The invention relates to a thread feed device for a hosiery knitting machine and more particularly for a hosiery knitting machine of the circular type.
There already exist numerous types of thread feed devices for circular hosiery knitting machines. The principal condition which these thread feed devices must satisfy is to supply a thread which has simultaneously a perfectly determined rate of feed and tension. To this end, various thread feed devices have already been proposed in which this condition is realized due to the fact that the thread, which arrives at the said device in a first state of tension, passes, after its entrance into the said device, into a second state, which state is known as intermediate tension, in which its tension is effectively greater than that which it had previously and where it is consequently drawn out, then finally, after having passed around a rotatably driven drum which controls the rate of feed of the thread, the thread is released so that its tension returns to a value less than that corresponding to the said intermediate tension.
But such thread feed devices which comprise at least one cylindrical positive drive drum for the thread, a series of toothed or axially grooved pulleys coaxial to the drive drum and on each of which turns a toothed or grooved drive belt driven by the motor of the knitting machine, a coupling element integral in rotation with the drive drum, but movable axially with respect to the latter to permit the choice of which toothed pulley will be coupled to the drive drum, have the disadvantage of being, on the one hand, difficult to operate and handle due to the fact that the coupling element between the drive drum and the toothed pulleys is purely mechanical, and, on the other hand, of being rather cumbersome due to the fact that the thread tension mechanism which they must also comprise is generally constituted by a second cylindrical drum.